Dependencies - move nette to optional dependencies

[f3l1x]

I'm also thinking about make this package thin as possible.

nette/application

Only usage is to create RedirectResponse, I vote for remove it a return only $url.

https://github.com/Markette/Gopay/blob/9a712df2cba8387a4b8c489bae44f2f8154037a5/src/Gopay/Service/PreAuthorizedPaymentService.php#L52

nette/forms

It is for bind some buttons/inputs to nette forms, but I don't use it and maybe other guys neither. So I vote for make it optional via require-dev.

nette/di

It's pretty standard and I don't see any reason to not include it.

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cc @haltuf @hranicka @Attanon

[haltuf]

ad nette/application: OK

ad nette/forms: never used this function, don't know what good could it be fore, to be honest